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Kamars can be an excellent tool to help detect estrus in cows and heifers if you know how to properly place them on the animal and accurately read the results. First, you need to make sure that you apply enough glue to the back of the Kamar so that it will stick to the cow. Next, you press it firmly onto the spine of the cow closer to the back if she is a tall cow and farther forward toward her hips if she is a shorter cow. The arrow should always be facing forward.
As you check for activated Kamars, you might notice some that are only partially activated. How do you handle those? Sometimes a partially activated Kamar means that the cow is just coming into estrus and has not been mounted enough times to fully activate the Kamar. Other times, it could be caused by a different cow that is in estrus and may have mounted that cow once or twice, even though she is not in estrus. Still another possibility is that the cow bumped her tailhead on the freestall, which could partially activate the Kamar as well. These are examples of why it is very important to only inseminate cows that have fully activated Kamars, which means that the entire strip is red. If a cow has been mounted numerous times, the Kamar may even develop a lighter red color and appear flattened. The key is that the entire Kamar is activated.
Source: El Companero